Just starting with new version 3. I'm put off by the note in the tutorial that warns against creating a style for body text because that might interfere with formatting during compile. But the recommended "no style" does not have any spacing after a paragraph. I dread working through my whole book with no white space between paragraphs. With the old presets, you could change font and spacing without impacting compile. What can I do now to create white space between paras?

This sort of thing is handled the same way it was in v2, except you can set the default formatting of text for just the project (see the Project->Project Settings menu) or for all Scrivener projects that don't have Project-level default formatting set via Scrivener->Preferences.

I suggest selecting 3 adjacent paragraphs, and then adjusting the paragraph spacing for them. Once you're happy with that, go to either Scrivener Preferences or Project->Project Settings and in the Formatting pane, click the "use Current" button to copy font & paragraph formatting.

Finally, select existing documents and use Documents->Convert->Text to Default Formatting... to update font & paragraph settings for all unstyled text. The aspects covered by paragraph or character styles will not be changed by this action (so Heading 1-styled text won't change font size or color, nor will it affect paragraph spacing for that text, for instance).